Zeolites are crystalline aluminosilicate compositions which are microporous and which are formed from corner sharing AlO2 and SiO2 tetrahedra. Numerous zeolites, both naturally occurring and synthetically prepared are used in various industrial processes. Zeolites are characterized by having pore openings of uniform dimensions, having a significant ion exchange capacity, and being capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal without significantly displacing any atoms which make up the permanent zeolite crystal structure.
The number of synthetic zeolites is well over a hundred as evidenced by the Atlas of Zeolite Framework Types published by the Structure Commission of the International Zeolite Association (IZA). As is well known, zeolites are distinguished from each other on the basis of their composition, crystal structure, catalytic and adsorption properties. One method commonly used in the art to distinguish zeolites is x-ray diffraction.
In U.S. Pat. No. 6,756,030 B1, a new family of materials designated UZM-8 is disclosed. The UZM-8 materials are zeolitic aluminosilicates ranging in Si/Al ratio from 6.5 to 35. They are prepared from reaction mixtures employing organoammonium structure directing agents with preferred examples being diethyldimethylammonium (DEDMA), ethyltrimethylammonium (ETMA), and hexamethonium (HM) cations and optionally alkali or alkaline earth metals and/or other organoammonium cations. The UZM-8 materials have a unique x-ray diffraction pattern and a composition on an as synthesized and anhydrous basis expressed by an empirical formula of:Mmn+Rrp+Al1−xExSiyOz where M is at least one exchangeable cation selected from the group consisting of alkali and alkaline earth metals, “m” is the mole ratio of M to (Al+E) and varies from 0 to about 2.0, R is at least one organoammonium cation selected from the group consisting of quaternary ammonium cations, diquaternary ammonium, protonated amines, protonated diamines, protonated alkanolamines and quaternized alkanolammonium, “r” is the mole ratio of R to (Al+E) and has a value of about 0.05 to about 5.0, “n” is the weighted average valence of M and has a value of about 1 to about 2, “p” is the weighted average valence of R and has a value of about 1 to about 2, E is an element selected from the group consisting of gallium, iron, boron, chromium, indium and mixtures thereof, “x” is the mole fraction of E and has a value from 0 to about 1.0, “y” is the mole ratio of Si to (Al +E) and varies from about 6.5 to about 35 and “z” is the mole ratio of O to (Al+E) and has a value determined by the equation:z=(m•n+r•p+3+4•y)/2.
Applicants have now modified these UZM-8 materials in order to change some of their properties. By using one or more techniques selected from acid extraction, calcination, steaming and ammonium hexafluorosilicate treatment, applicants have been able to control the aluminum content of the UZM-8 zeolites to nearly all silica while maintaining their structure and porosity. Dealumination strategies are known in the art and are given by Breck (see D. W. Breck, Zeolite Molecular Sieves, Wiley and Sons, New York, (1974), p. 441) and Skeels and Breck (see U.S. Pat. No. 4,610,856). The result is a modified UZM-8 (UZM-8HS) material containing less aluminum than the starting UZM-8 composition. Control of the Al content in the zeolite allows one to tune the properties associated with the Al, such as ion-exchange capacity and acidity thereby providing improved catalysts and/or adsorbents. This new family of materials is designated UZM-8HS.